The field of optical communications, that is communication using optical fibers, transmitters, receivers, modulators and amplifiers, is becoming more mature and cost competitive. Additionally, in order to manage the increasing demand for bandwidth over an optical fiber, it has become necessary to introduce a technique know as Wave Division Multiplexing (WDM).
WDM technology comes in two basic forms. These include Coarse WDM (CWDM) and Dense WDM (DWDM). Both work in the optical domain, very similar to frequency division multiplexing in the electronic domain. Instead of using a single laser (i.e., single color or wavelength) to communicate across a fiber optic network, WDM uses several different wavelengths to increase the capacity of a single optical fiber by modulating each color with a different data signal and hence increasing the capacity of a single fiber by the number of colors or channels it can carry simultaneously.
By increasing the number of colors carried by a single fiber the number of channels and hence the bandwidth of the fiber is increased. However the traditional method of increasing capacity involves providing transmission ‘pairs’, each pair comprising one path or wavelength to transmit and another path or wavelength to receive. In some applications, this may not be the ideal provisioning scheme as it limits the traffic in each direction to be approximately equal.
Referring to FIG. 1 it can be seen that the number of channels going from left-right and those running from right-left are fixed and remain in an assigned direction. In particular, FIG. 1 shows a four wavelength (color) channel communication fiber with two colors (λ1 and λ2) traveling down the fiber in a first direction (i.e., left to right) and a two colors (λ3 and λ4) traveling down the fiber in a second, opposite direction (i.e., right to left).
On the left hand side of FIG. 1, a laser driver 10 modulates a data stream 12 to drive a laser 14 producing a beam having the wavelength λ1. The beam λ2 is produced in a similar fashion. The beams are wavelength division multiplexed using for example an array waveguide grating (AWG) 16, and travel as a multiplexed beam across a fiber 18. A similar AWG 20 on the right hand side of the communication channel 18 demodulates the beam into the individual wavelengths (λ1 and λ2) where they are received by respective photo detectors 22 and amplified by their respective amplifiers 24 to output the original data stream 12. Data channels λ3 and λ4 work in a similar fashion, only traveling in the opposite direction from right to left.
A drawback to the above design is that the direction a particular channel travels is fixed. This means that unless the original network designers anticipated that an asymmetric traffic profile is warranted, the normal implementation involves assigning an equal numbers of channels (wavelengths) in each direction. However, due to local traffic conditions or circumstances, it may be desirable to provide an asymmetric path between nodes such that, say, the right-left direction can carry more traffic that the left-right direction.
A practical reason for desiring an asymmetric network may be demonstrated by considering the download of a music file or picture file from the World Wide Web (WWW) where the data requesting the song (title, artist, URL etc.) is many times smaller than the downloaded data itself. The effect of this asymmetric demand for bandwidth is that the network provider typically over provisions the upstream paths in order to meet the demands of the downstream paths.
A need may exist to dynamically to permit asymmetrical and programmable bandwidth over an optical fiber in either direction.